I have to ask regarding this topic - is there any simple way to overcome the 23:18 video issue (video locks up after 23 minutes) in firefox 52.9.0 with hardware acceleration?
I have tested many different graphics cards: HD5770, HD7850, GTX970, GTX770, GTX660, GTX780Ti, HD6950 and it only really (reliably) worked with HD7970 GHz ed. I guess firefox requires serious shader power to play long youtube videos reliably/without stalling... :-(